Question: Tiffany is 4 times as old as Kevin and is also 9 years older than Kevin. How old is Tiffany?
Solution: We can use the given information to write down two equations that describe the ages of Tiffany and Kevin. Let Tiffany's current age be $t$ and Kevin's current age be $k$ $t = 4k$ $t = k + 9$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $t$ is to solve the second equation for $k$ and substitute that value into the first equation. Solving our second equation for $k$ , we get: $k = t - 9$ . Substituting this into our first equation, we get the equation: $t = 4$ $(t - 9)$ which combines the information about $t$ from both of our original equations. Simplifying the right side of this equation, we get: $t = 4t - 36$ Solving for $t$ , we get: $3 t = 36$ $t = 12$.